Sen. Elizabeth Warren (D-MA) on Thursday called on the Department of Homeland Security Inspector General to open an investigation into private prison contractors that have been accused of breaking a landmark human-trafficking law. Warren’s request follows a Daily Beast report that the GEO Group, the nation’s second-largest private prison company (and an ICE contractor), has been repeatedly sued by former detainees over a so-called “voluntary” work program. The lawsuits allege that GEO forces inmates to do manual labor for $1 a day, or even less, and sometimes punishes those who refuse with solitary confinement.

“The GEO Group, Inc. (GEO) and CoreCivic, the two largest for-profit, federally-contracted prison companies, which ICE contracts to house immigrant detainees along the U.S. southern border, face several lawsuits alleging the use of punishment as a tool to coerce detainees into voluntary work programs,” Warren wrote in a press release. “... GEO’s private claim that ICE policies require, recommend, or allow the use of solitary confinement to coerce participation in a ‘voluntary’ work program is alarming.”